Re: [Xen-devel] Debug guest state (VMI)

[George Dunlap <dunlapg@xxxxxxxxx>]

On Mon, May 28, 2018 at 4:24 PM, Mathieu Tarral
<mathieu.tarral@xxxxxxxxxxxxxx> wrote:
> Hi !
>
> I'm playing with the VMI APIs using LibVMI, and i need to track down
> a bug that i reported here:
> https://github.com/libvmi/libvmi/issues/621
>
> Basically the domain is still paused even thought i called the right API
> to resume it and the event buffer is supposed to be empty.
>
> Now there are 2 possibilities
> - either there is an event in the buffer waiting to be processed
> - or the resume_vm function failed
>
> Is there a way to track the state of the guest VMI event buffer ?
> (what events are registered)

I think what Tamas was asking you to do was to add that tracking yourself. :-)

Two basic approaches:

1. Add printk() calls to the appropriate code.  This is fairly
straightforward and intuitive (once you find the code and figure out
what it's doing), but if there are a lot of printks it slows
everything down a lot.

You *can* use `xl dmesg` for these, but
https://wiki.xenproject.org/wiki/Xen_Serial_Console is recommended.

2. Add xen trace events.  Use xentrace in dom0 to record them, and
xenalyze to look at the results.

This takes a bit more work, as you need to marshall the information
you want into trace records, and then out again (in xenalyze).  But it
has the advantage that you have a lot more information about which
process was running where at the time, and it makes it much easier to
deal with large amounts of events.

Either way, you're going to really need to get your hands dirty, so good luck.

 -George

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